Piezoelectric crystal system



Feb. 20, 1951 E. l.. MINNlcH PIEzoELEcTRIc CRYSTAL SYSTEM 4 Sheets-Sheet l Filed March 7, 1949 gg l@ l? L, ik

E. L. MlNNlCH PIEZOELECTRIC CRYSTAL SYSTEM Fgb. 2o, 1951 Filed March 7, 1949 INVENTOR.

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E. L. MINNICH PIEZOELECTRIC CRYSTAL SYSTEM Feb. 20, 1951 4 Sheets-Sheet 5 Filed March 7, 1949 44 :linfa-...1E- 4535!! 457 )55 INVENTOA /wam) 'Qa 9W? Q29 Tuvm Feb. 20, 1951 i E. l.. MINNlcH PIEzoELEcTRIc CRYSTAL SYSTEM 4 Sheets-Sheet 4 Filed March 7. 1949 nnnn vllvlllllivnrvlllllrn'flr-v,n.

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Patented Feb. 20, 1951 PIEZOELECTRIC CRYSTAL SYSTEM Edward L. Minnich, Carlisle, Pa., assignor to Selectronics, Inc., Carlisle, Pa., a corporation of Pennsylvania Application March 7, 1949, Serial No. 79,939

7 Claims.

My invention relates broadly to piezo electric crystal apparatus and more particularly to a construction of multiple piezo electric crystal holder and mounting means for associating the crystals with electrical circuits.

One of the objects of my invention is to provide an improved mounting means for a multiplicity of piezo electric crystals of different frequency characteristics which may be associated within an extremely small and compact area and selectively employed for controlling various electrical circuits.

Another object of my invention is to provide a mounting means for a multiplicity of piezoelectric crystals within a metallic housing including means for electrically shielding the crystals and capacitatively relating the shielding means tothe associated mounting means in such a manner that certain electric condensers normally required in the co-acting electric circuits may be omitted and eliminated, thus saving cost in production of electrical apparatus employing such circuits.

Another object of my invention is to provide a means for mounting a multiplicity of piezo-electric crystals with respect to a supporting plateY within a single metallic housing sealed to this supporting plate in a manner that the presence of dust,fmoisture, and gases will have no effect on the operating functions of the crystal within this metallic housing.

Still another object of my invention is to provide a means for mounting` a multiplicity of piezo electric crystals with respect to a supporting plate within a metallic housing in such manner that thecrystals are closely associated and yet electrically insulated one from the other for individual selection and operation in co-acting electrical circuits.

Other and further objects of my invention reside in the construction of mounting means for piezo electric crystals as set forth more fully in the specifications hereinafter following by reference to the accompanying drawings, in which:

Figure 1 is a top plan view of the multiple piezo electric crystal holder of my invention; Fig. 2 is a longitudinal sectional view through the multiple piezo electric crystal holder taken substantially on line 2`2 of Fig. 1 and Fig. 4; Fig. 3 is a longitudinal sectional View through the multiple piezo electric crystal holder taken substantially on line 3-3 of Fig. 1; Fig. 4 is a transverse sectional view taken substantially on line 4-4 of Fig. 1; Fig. 5 is a schematic Wiring diagram illustrating the manner of selecting the individual piezo electric crystals in the multiple piezo electric crystal ap paratus of my invention; Fig. 6 is a perspective view of the multiple piezo electric crystal holder showing the parts of the holder in juxtaposition ready for assembly in a compact assembly; Fig. '7 is a transverse sectional view taken through the assembled piezo electric crystal holder shown inY Fig. 6 with the parts assembled, the view` being taken substantially on line l-l of Fig. 6; Fig. 8 is a perspective view showing the capacitor ele-- ment employed within the casing of the apparatus; Fig. 9 is a schematic view showing the circuit arrangement by which certain condensers in the oscillator are compensated for and omitted or eliminated by-use of the construction of multiple crystal holder of my invention; Fig. 10 is a top plan view of a modied form of multiple piezo crystal apparatus employing my invention in which individual insulators are employed for insulating the piezo electric crystals from the metallic housing of the piezo electric crystal appa--A ratus; Fig. 11 is a longitudinal sectional viewY taken substantially on line II-l I of Fig. 10 andk Fig. 13; Fig. 12 is a longitudinal sectional view through the multiple piezo electric crystal apparatus taken substantially on line |2-I2 of Fig. 10 and Fig. 13; Fig. 13 is a transverse sectional. view taken substantially on line l3-I 3 of Fig. l0; Figs. 14, 15 and 16 show modified arrangements. for fixing the effective capacity of the capacitor that is built into the multiple crystal holder by spacially relating the capacitor strip by differing` dimensional amounts with respect to the casing; Fig. 17 is a perspective view of the piezo electric crystal apparatus shown in Figs. 10-13 with parts broken away to illustrate the internal construc tion more clearly; Fig. 18 is a transverse sectional view through a modied form of multiple; piezo electric crystal apparatus embodying my. invention; Fig. 19 is a fragmentary longitudinal sectional View taken substantially on line lli-I 9 of Fig. 18; and Fig. 20 is a horizontal sectional view taken substantially on line 2& 26 of Fig. 18. I have developed the apparatus of my inveni tion to meet the requirements of electronic apparatus employing multip-le piezo electric crystals. In certain forms of radio broadcast re ceivers a multiplicity of piezo electric `crystals are employed of the order of twenty-one or more. l The problem of mounting such crystals within the allowable extremely small area in such manner that adequate insulation is assured for the individual crystals is a very severe one. I have shown a multiple piezo electric crystal holder herein in which the overall length of the casing 3 constituting the crystal housing for housing eleven crystals is but 41%, while the overall width of the casing is but llg", and the heighth is but I provide a construction of multiple crystal holder which assures adequate insulation for the individual piezo electric crystals within the casing which forms an electrical shield. Acapacitor member is built into-the piezo electric crystal holder and electrically connected with one side of each of the piezo electric crystals and spacially related to the electrical shield constituting the casing. This arrangement when connected with an electron tube oscillator circuit completes a capacitative feed-back path for the oscillation circuit, thereby enabling the feed-back condenser normally required in the oscillation circuit to be omitted and eliminated. This reduces expense in manufacture and production of radio broadcast receivers of the multiple piezo electric crystal type lwhich in a mass production program may involve lvery sizeable amounts. The apparatus of my invention l*involves novel mounting means f or the `individual piezo electriccrystals by which adequate support of each of the piezo electric crystals within the shielded housing is assured in a very practical manner. I may employ piezo electric crystals of various cuts and types as typified ,for example by the circular crystal of Fig. 4 or the rectangle crystals of Figs. 6, 7, 13 and 17, 18,19 and 20.

Referring to the drawings in detail, reference character I designates the metallic shielding container or tank having an open supporting or top peripheraledge 2 with a closed metallic bottom 3. :Extension lug members 4 and 5 are secured to opposite ends of the external face of the closed bottom 3 .of the .shielding container I. The lugs 4 .and 5 each contain apertures 4a and 5a that permit the passage of securing screws 6 and 1 which extend through .the washers 8 and 9 and enter the supporting surface such as the chassis of .associated electronic apparatus, which may hea radio receiver and the like.

A panel formed from insulation material I Il having a peripheral flange I@ thereon enters theopenend 2 `of the tank I and is secured with respect to the tank I by appropriate securing screws I-I. I mount a multiplicity of terminal posts I2 corresponding Yin number to the number of .piezo electric crystals supported in the holder on the lpanel of insulation material IIJ in a row extending longitudinally of the holder Aas shown inFigs. l and 2.

In .positions transversely opposite each of the end terminal posts in the row of terminal posts I2 I provide terminal posts I4 insulatingly and spacially related thereto. Terminal posts I4 serve as supports and electrical connectors for the capacitor strip I which rextends longitudinally of the casing I. The strip I5 is formed from metal stock approximately .040 to .050 thick and 1A Wide, In the dimensional example heretofore given .this strip is approximately 4 in length. In `the form of my invention shown in Figs. 1-8 the capacitor strip I5 is in the form of an angle with one side thereof, approximately 1A" wide, extending in spacial capacitive relation with the side of metallic container I. This forms a condenser in the circuit path of each of the crystals. Small studs I6 are welded or otherwise secured to strip I5 and project therefrom in an upright position serving as supports for springs I1. In the dimensional example heretofore referred to these studs are spaced approximately apart 4 which permits mounting of a plurality of spaced crystals within the container I without mutual contact. Springs I'I connect with one of the ends of the several piezo electric crystals I8 shown in Fig. 4 and establish electrical and mechanical connection with electrode I9 thereon. The other ends of the piezo electric crystals IB are supported `in `springs 20 projecting from Vterminal posts I2 and establishing electrical and vmechanical connection with electrodes 2| on the opposite faces of the crystals.

The terminal posts I2 and I4 have annular flanges thereon that are embedded in the insulation .material of panel E0 for solidly anchoring the .posts in thepanel. The posts I2 and I4 project through the material of panel IU and provide external connection means to the electronic oscillator system outside of the casing I. The terminal posts I4 adjacent opposite ends of casing I serve as both electrical connecting means andmechanical supports forthe strip I 5.

The springs `IFI and ,2.0 which serve as supporting-members for the-individual piezo electric crystals I8 comprise Ycoils of spring wire -I'Ia and 20a which respectively.embrace'the inwardly directed studs V:II and the Vinwardly directed terminalrposts I2. The other ends of springs I'I and A2l) atei-minate in looped or coiled vends'I'Ib and20b disposed in the same plane .in spaced positions within .the container l `to grip the electrodes .of the pieno electric crystal I8 therebetween.

Each piezo electric crystal I8 has :theopposite conductive electrodes I9 'and 2.I which are -secured vto opposite faces of :the piezoelectric crys tal intimately .connected with the ispring wire loops or coils lIIb `and 20h by low-meltingpint metal which assures a rigid mechanical support between :the spring wires I'I and 20 and the vpiezo electric crystal .I8 Aand a highly conductive .electrical connection with the .electrodes I9 and :2l of the crystal I8. This connection is so sturdy and reliable that even though the multi-ple piezo electric crystal holder is subjected to very fsubstantial `vibration or in fact, lmechanicalshock. the .crystals are ,retained in the gripof the spring Wire coils or loops I'IZ) and 20h.

In Fig. 5 I have illustrated the circuit arrangements for the piezo electric crystal elementsfrom which it will be noted that one longitudinal row of terminals is constituted `by capacitor Istrip I5, capacitatively related to the metallic vwall ofecentainer `I which is grounded at 22. `Theother row of .terminals is constituted by spaced terminal posts I2 which individually connect with the opposite Isides of each .of ,the `piezo electric crystal elements. The several piezo electric crystal elements .connect to contacts varranged compactly in the arc of 4a circle las represented at 23, over which the switch arm 24 operates to select aparticular piezo 'electric crystal from the group r:of piezo electric crystals I. In Fig. 5 `I have schematically shown only five piezo electric crystals but it will be understood that any multiple number of such elements may be employed.

In Fig. 6 I have shown'the shielded containerl, removed from the panel I0 of insulation material and disposed in juxtaposition with respect there to, and showing in perspective view the-piezo electric crystal elements which are'normally'housed within Ithe container. The piezo electric crystal! elements in this arrangement are rectangular, as shown at |84, instead of circular as shown in Fig. 4 at I8, but all other details are arranged `as explained in connection with Figs. 1 5. The `posts I2 in Athis arrangement are illustrated as having solder lugs 25 connected to the externally projecting stems of the terminal posts land extending in spaced relation beyond the periphery of the panel IIJ for permitting individual electrical connection to be readily made thereto. The electrodes on the surfaces of the piezo electric crystals are arranged in a manner explained in connection with Fig. 4 but by reason of the rectangular shape of the crystals the electrodes are elongated as represented at i3d and 2Ia of Figs. 6 and 7.

Fig. 7 illustrates on a somewhat larger scale the manner in which the rectangular piezo electric crystals are spacially disposed within container I while capacitative coupling is established between strip I and the metallic wall of container I.

In Fig. 9 I have represented the electrical circuit of the electron tube oscillator which is associated with the multiple piezo electric crystals Within the container i. The metallic Wall of the metallic container or tank I forms one capacity area of an electrical condenser in co-action with the capacitor strip I5. Electron tube oscillator 26 is schematically shown as including cathode 26a, control grid 26D and an anode 26e. The control grid 23h is connected in the input circuit of the oscillator through the impedance 21 to ground 22. Cathode 23a is connected through impedance 28 to ground 22. Anode 23e is connected with the output circuit of the oscillator including radio frequency choke coil 23 and high potential source indicated at 3i), and ground connection 22. The piezo electric crystal element represented at I8, I8', I8, etc. have the electrodes IS, I9', I9" etc., thereof, respectively connected to capacitor strip I5.

The electrical capacity between electrodes I9, I9', I9 and the metallic container I is established by the spacial relation of metallic strip I5 and the metallic wall of the container I. The electrical capacity thus provided constitutes a feed-back path for oscillations between the input and output circuits of the oscillator 26. This capacity compensates for and takes the place of an external condenser which must normally be included in the input circuit of the oscillator in shunt With impedance 21 in the input circuit. Accordingly, by spacially relating capacitor strip I5 to metallic container I internally of the container, the essential feed-back capacity may be provided between l the input or output circuits cf the oscillator without the necessity of installing the separate condenser normally required. This results in a very appreciable saving in a manufacturing and production program Where many thousands of such condensers would be required.

In Figs. 20 I have shown a modiiied form of multiple crystal holder embodying my invention inwhich the metallic housing 3! is substituted for the shielding container or tank I. The metallic housing 3l has a peripheral bead 32 adjacent the extremity of the edge thereof which provides a peripheral seat for the inverted metallic pan member 33.

The inverted metallic pan 33 is peripherally supported by the peripheral seat 32 when the pan 33 is frictionally forced into the housing 3|. The pan 33 forms a support for the multiplicity of. piezo electric crystal elements. In this arrangement one row of piezo electric crystal element supports represented by the resilient wirelike spring elements 34 are attached by coils 34a to studs 35 depending from capacitor strip 36 and terminate in loops 34h which embrace the ends of piezo electric crystal elements IBb for establishing electrical connection with the elec-f trode surface I9b and 2Ib as represented in Fig. 13. The capacitor strip 36 is insulatingly and spacially mounted with respect to pan 33 by means of terminal posts 44 that pass through bushings 31 of insulation material supported in sleeve-like bushings 38 extending through the pan- 33. A common terminal connection for the container 3| projects from the rear of pan 33 as shown at 39. The co-acting opposite terminals for each of the multiple number of piezo electric crystal elements are insulated from the metallic pan 33.

Terminal posts 4B individual to each of the resilient wire-like members 4I are gripped by the coiled ends 4 Ia of the resilient wire-like members 4U as shown in Fig. 13. The terminal posts 40 pass through bushings formed by insulation material 42 carried in sleeve-like members 43. The sleeve like members 43 each have annular flanges 43a thereon and are seated in a longitudinally extending row of apertures provided in pan 33. The insulation material 42 is vitreous or is formed from composite insulation material and substantially insulates terminal post 4B from contact with metallic sleeve 43 or metallic pan 33. The terminal posts 40 project beyond the peripheral limits of pan 33 and enable electrical connections to be made thereto for completing circuits to the individual piezo electric crystal element-s.

The opposite extremities of the metallic housing 3| or the pan 33 may be rolled over to provide a peripheral interlocking joint, or spaced lugs 45 may be provided on housing 3i and may be rolled over the peripheral edge of pan 33 to secure pan 33 is position against peripheral seat 32 and within housing 3 I.

The same method of mounting the metallic housing 3l is provided as is employed in the arrangement of Figs. 1-8; that is, lugs 4 and 5 are perforated at 4a and 5a for the passage of securing screws.

The electrical capacity referred to in Fig, 9 is inherently provided in the multiplepiezo electric crystal holder of Figs. .l0-13, eliminating and replacing feed-back condenser normally required in the oscillator circuit. In order that different values of capacity may be provided Within the crystal holder I may selectively fix the length of insulation bushings 31 as represented in Figs. 14, 15 and 16 to x `the spacial relation of capacitor strip 36 and the metallic pan 33. For example, the short bushing 31 in Fig. 14 provides a relatively high capacity value; the bushing 31 of greater length shown in Fig. l5 provides a capacity of lower value, while the bushing 31 of the longest length as shown in Fig. 16 provides an effective capacity within container 3l of the smallest value.

The manner of supporting the piezo electric crystals in the form of my invention illustrated in Figs. 10-13 is the same as that described in connection with the form of my invention Shown in Figs. 1-8, and I have applied similar reference characters to vcorresponding parts of the crystal and the electrodes thereof by adding the subscript a to the crystal and the electrodes thereof.

In Figs. 18-20 I have illustrated a further modiiied form of multiple crystal holder in which a metallic housing 46 is provided, closed on all sides except one which is closed by a metallic pan 41 having a peripheral edge 48 operative to engage the edge of housing 46. The pan 41 is apertured in transverse aligned positions at 49 and 50 with outstruck sleeves 49a and 50a co-extensive with the pan 41; The sleevesvdaand 56al are* filled with insulation material and 52 forming supports for the pin members 53 and 54.

The pin members 53 and 54 each'carry` spring st'ripson the ends thereof' as represented at.55 and' 56. The spring strips 55 and! 56 areeach folded upon themselves to form spring'clamping jaws 51 and 58. These Spring clamping jaws grip andengage opposite sides of the piezo electricv crystal which in this instance is represented by` reference character 59 with opposite electrodes 60 and 6|- thereon. The electrodes Ell-.and Blox-v tend from the center of crystal 59 to opposite.

mentsare maintained in position and cannot beV accidentally or readily shaken or displaced from the securing means.

The capacitor strip G2 is mounted on pin members 5,3 spaced from pan il by the insulation supports 5I inicapacitative relation to the underside of` pan el; Anv electrical circuit grounded to the metallic housing #l inherently places the electrical capacity existent between the ground and one of the electrodes of the piezo electric crystals in shunt with the input circuit of the oscillator in the manuel' explained in connection with the circuit of Fig. 9.

With the advent of piezo electric crystal apparatus` functioning on many closely adjacent frequencies in multiple signaling channels, the importance of the multiple piezo electric crystal apparatus of my invention will be appreciated. The large `number of individual piezo electric crystal elements of different frequency characteristics may be mounted within an extremely small space on racksor adjacent an apparatus chassis for eflicientlyl providing for the selective operation of numerous electrical circuits on closely adjacent frequencies.

One of the advantages arising out of the application ofthe multiple crystal holder of my invention results from the fact that it is diiiicult and costly to nish a crystal to a precise fren quency, and the wider the finishing tolerance;

the lower the production cost. Crystals'which cover the broadcast band may be ground to a relatively Wide finish frequency tolerance by cone trolling the amount of plating on the surfaces rof the crystals, and then grouping or classifying these crystals as tothe number of cycles to which they maybe high or low with respect to the pree cise frequencyor desired frequency. The cryse tals may be classified in at least three groups, as

being high, medium (or on), and low, and may include two other classiiications, as extremely high and extremely low frequency tolerance crystals.

An` oscillator circuit does have some influence on the' frequency of the crystal, and if the grid to ground capacity of a Pierce oscillator, forexample, is varied thefrequency is changed appreciably and may bring the crystals into tolerance, providing they are finished at some frequency not toofar removed from the desired frequency. If

the crystalV ishigher than the ldesired frequency the" capacity would be 1 increased' acrossl the gridrl tov ground; Conversely, if thecrystal frequency is lower than the desiredfrequency, the capa/cityAV is reduced.

Froml the foregoing it will be understood' that the holder maybe made in three to five stepswith respect to the value of this built-in capacitor,`

which is connected between the grid of the-oscil lator and the ground. The crystals'V noted' as high or extremely high are put in holders` with the maximumy value of inbuilt capacity.

The crystals classied as low or extremelyY lowiare put in a holder with the minimum ca-zpacity, and those crystals classified as "medium"' or on'would go into a holder with an averagek or medium value of capacity. As hereinbelorer stated this makes the finishing operation a little moresimple, thereby reducing manufacturing.'

costs. This is a substantial advantage to thek crystal manufacturer and can be passedv on to the customer in lower price.

While I have described my invention in certain.

of its preferred embodiments I realize that modi.-

caticns may be made in the arrangement of.' i parts and elements of the apparatus and I' desire. that it be understood thatno limitations upon my invention are intended other than may beim", posedby the scope of the appended claims.

What Iclaim as new and desire to secure byV Letters Patent of the United States isas follows: l. A multiple piezo-electric crystal apparatus'.`

comprising inA combination, a metallic. electr-is cally conductive housing closed. on all. sides ex-f cept one, a platemember of insulation material. fitting into the open side of said housing, a mul-Y tiplicity of supports projecting from said plate member in spaced, substantially parallel relation into a position interiorly of said housing, .a .multiplicity of piezo electric crystal elements carried by said supports and terminal members extend.- ing. from said supports to a position externally of said housing for providing an electrical connection with said piezo electric.crystalelements.

with-saidpiezo electric crystal elements.

3. Inf a multiplepiezo electric crystal holder; an electrically conductive housing openat oneA side thereof, a supporting base of insulating ma.-

terial closing said open'A side, a pair of spacedl terminal members carried by said base, a metallic member disposed withinsaid housing and hav-- ing a plane surface extending substantially par-v allel to one of the inner facesr of said eiectrically,N

conductive housing,` pin members projecting` from said member, resilient wire-like members secured to saidpin members, resilient loops on' the ends of said wire-like members, independent terminal members mounted on said basaresilient wire likev members' secured to said independent terminal: members, resilient loops: on

said last mentioned wire-like members, andpiezo"l electric crystals having oppositeelectrodes grippcd by said resilient loops.

9 members, resilient wire-like members carried by said pins, resilient loops on said wire-like members, coacting terminal members embedded in said base, a metallic strip mounted on said last mentioned terminal members and having a coextensive portion disposed in substantially parallel spaced relation to a portion of said electrical shield, pins carried by said strip, resilient wire-like members carried by said last mentioned pins, resilient loops on said last mentioned wire- -like members directed toward said rst mentioned resilient loops in coplanar relation thereto, and piezo crystals having electrodes on opposite faces thereof gripped between said loops and establishing electrical connection with the respective terminal members.

5. In a piezo electric crystal holder a metallic housing open at one side thereof, a metallic base telescopically engageable within the open side of said metallic housing, terminal members insulatingly supported in said metallic base and projecting into said metallic housing, a capacity area carried by one of said terminal members in a position inside said metallic housing and spacially related to said metallic base, a piezo electric crystal having electrodes on opposite faces thereof and resilient engaging means carried by said terminal members for supporting and establishing electrical connection with said piezo electric crystal, said capacity area forming with said metallic base a predetermined electrical capacity.

6. In a multiple piezo electric crystal holder, a metallic housing open at one side thereof, a metallic base telescopically engageable Within the open side of said housing, a longitudinally extending linear row of bushings of insulation material projecting through said metallic base at spaced intervals, metallic terminal members projecting through the bushings in the said row and directed inwardly into said housing, resilient means on the ends of said terminal members, a pair of bushings of insulation material disposed in said base in spaced transverse alignment to the aforesaid bushings, separate metallic terminal members disposed in said last-mentioned pair of bushings, a metallic member supported on said last-mentioned terminal members and insulated from said metallic base, resilient means 10 supported by said metallic member and directed inwardly into said housing and respectively in transverse alignment with the aforesaid resilient means, and piezo electric crystals extending transversely of said housing and gripped in mechanical supporting and electrical relation by said resilient means in closely adjacent substantially parallel planes.

7. In a multiple piezo electric crystal holder, a metallic housing open at one side thereof, a metallic base telescopically engageable within the open side of said housing, two longitudinally extending rows of bushings of .insulation material projecting through said metallic base, the bushings in one of said rows being disposed at spaced intervals, while the bushings in the other row comprise a single respective bushing in transverse alignment with the end bushings in said first-mentioned row, metallic terminal members projecting through the bushings of said rstmentioned row and directed inwardly into said housing, separate metallic terminal members disposed in the bushings of the other of said rows in transverse alignment with the end terminal members in said first-mentioned row and insulated from said metallic base, a capacitor strip mounted on said last-mentioned terminal members and extending in spaced substantially parallel insulated relation to said metallic housing, resilient means supported by each of said terminal members and said capacitor strip, and piezo electric crystals extending transversely of said housing and gripped in mechanical supporting and electrical relation by said resilient means in closely adjacent substantially parallel planes.

EDWARD L. MINNICH.

REFERENCES CITED The following references are of record in the 

